1. Field of the Invention
The present invention relates to a data transfer controller for controlling the timing for transferring display data to a plurality of display devices.
2. Background Information
In recent years there has been an increase in electronic devices provided with a display device, such as portable telephones and on-board AV devices and the like. These electronic devices are provided with a data transmission controller for controlling the timing for transmitting display data, and a data transmission device for transmitting the display data in order to display the display data such as images and the like on a display device.
FIG. 11 shows an example of a system for transferring display data to a single display device. The system of FIG. 11 is configured by a data transfer controller 501, memory 502, data transfer device 503, and a single display device 504. The data transfer controller 501 outputs the vertical synchronization signal of the display data. The data transfer device 503 transfers display data to the display device 504 based on the vertical synchronization signals from the data transfer controller 501. The transferred display data are received by a data receiver 541 provided in the display device 504, and are displayed on the display device 504.
Electronic devices have become diversified in recent years, and electronic devices provided with a plurality of display devices 601a˜c have especially proliferated, as shown in FIG. 12.
Japanese Laid-Open Patent Publication No. 06-292200 discloses a data transfer device corresponding to each of a plurality of display devices in order to transfer display data to a plurality of display devices. FIG. 13 shows an example of the system of Japanese Laid-Open Patent Publication No. 06-292200. Specifically, data transfer devices 703a˜c are provided in correspondence with the display devices 704a˜c. The data transfer controller 701 outputs the vertical synchronization signals of the display data to the data transfer devices 703a˜c. The data transfer devices 703a˜c transfer display data to the display devices 704a˜c in synchronization with the vertical synchronization signals A, B, and C. This time the data transfer controller 701 transfers the same vertical synchronization signal to the respective data transfer devices 703a˜c. Therefore, the timing for transferring display data to the display devices 704a˜c is identical for all of the data transfer devices 703a˜c. 
In the method disclosed in Japanese Laid-Open Patent Publication No. 06-292200, all data transfer devices 703a˜c simultaneously transfer display data to the respective display devices 704a˜c, and simultaneously stop transferring display data. The power consumed by each data transfer device 703a˜c during the transfer of display data (hereinafter referred to simply as “power consumption”) is designated [P]. As shown in FIG. 14, in the period during which all data transfer devices 703a˜c are simultaneously transferring display data, the total power consumption of the data transfer devices 703a˜c is designated [3×P]. In the period during which all data transfer devices 703a˜c simultaneously stop transferring display data, the total power consumption of the data transfer devices 703a˜c is designated [0]. In this way the total power consumption fluctuation range can be described as 3×P−0=3×P.
Although the method disclosed in Japanese Laid-Open Patent Publication No. 06-292200 is suitable when displaying still images on a display device, it is unsuitable when displaying video images. When displaying video images, display data are updated with greater frequency than when displaying still images. Therefore, when displaying video images, the period during which display data are transferred must be shorter than when displaying still images. When shortening the period during which display data are transferred, the clock frequency for displaying the display data may be increased. Then, the pitch in the fluctuation of the power consumption of the data transfer devices 703a˜c also increases due to the high speed of switching between the period during which display data are transferred and the period during which the display data transfer is stopped.
The fluctuation in power consumption of the data transfer devices 703a˜c becomes power source noise of the power source used by the data transfer devices 703a˜c. The power source noise also becomes noise in the transfer display data. Noise readily appears in display data particularly when the clock frequency is high as in the case of video images. This phenomenon must be considered particularly when display data are transferred by an AV device installed in an automobile because there is a possibility that the display data noise may adversely affect other automobile components such as the engine and brake systems and cause errors in operation.
The present invention controls the timing for transferring display data so as to reduce the power consumption of the data transfer device and suppress the previously mentioned fluctuation which causes noise in the display data.
In view of the above, there exists a need for a data transfer controller which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.